Such saw mills generally include a frame which straddles a log to be milled. The frame will typically include a pair of rails or tracks which in use extend longitudinally along the log. A carriage is mounted for movement along the rails or tracks. The carriage typically carries an engine, gearbox and saw blade. The saw mill can be of a swing blade type which permits the blade to be moved to vertical and horizontal positions so that vertical and horizontal cuts can be made in the log as the carriage is moved along the rails or tracks.
A sawing device comprising a saw blade, which pivots through 90° to act in both the horizontal and vertical planes, is known. In such a sawing device, the saw is moved along the length of the material. Permanent and portable versions of such saw mills are available.
As can be appreciated, movement of the saw blade relative to the material being sawn, in any direction other than the desired cut direction, is undesirable. For instance, when making a longitudinal cut, either vertically or horizontally, movement of the blade in and out of the cut is to be avoided. If this form of shake, or bounce, can be avoided a significantly improved finish is possible on the sawn material and the tooth life of the saw blade will be lengthened.
The problem of bounce is particularly pronounced in portable saw mills, since the power head (which includes an engine, gearbox and saw blade) is not supported by as heavy or sturdy a frame as in the permanent saw mill. That is, the frame on which the saw blade is mounted provides less resistance to bounce in a portable saw mill.
Portable saw mills generally include a frame which straddles the material to be sawn. A carriage mounted on the tracks, and which carries the power head, allows movement of the saw blade along the material to be sawn. The track is typically a pair of rails that can be positioned vertically so that the depth of a vertical cut by the saw blade can be set. The depth of any horizontal cut is controlled by moving the frame, on which is mounted the power head and the saw blade, relative to the material to be sawn. Increasing the depth of the cut, and/or the length of the tracks between the ends pieces, each independently increases the likelihood of shake or bounce.
A well known portable saw mill of this type is described in Australian patent 688020, the disclosure of which is incorporated herein by way of specific reference. When such a device is used to make a vertical cut, one problem is that the saw blade moves up and down vertically as the carriage bounces. The result is that the saw blade intermittently comes off the floor of the vertical cut, which stresses the teeth of the saw blade and results in the depth of the cut being uneven. When such a device is used to make a horizontal cut, one problem is again that the saw blade moves left and right.
The invention will be described with reference to portable saw mills but the skilled person will appreciate its applicability to permanent saw mills in certain circumstances. The object of the invention is to reduce the above-described undesirable movement of saw blades in saw mills.
Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.